The human milk oligosaccharide lacto-N-neotetraose (LNnT) has previously been crystallized. Kuhn et al. [Chem. Ber. 1962, 95, 513, 518] originally isolated LNnT from a natural source and crystallized it (referred to as “LNnT polymorph I”). EP-A-1405856 disclosed that crystals of LNnT were obtained from aqueous acetone and proved by X-ray powder diffraction data (referred to as “LNnT polymorph II”). WO 2011/100980 disclosed another polymorph of LNnT having different melting point from that of Kuhn's crystals and a different X-ray powder diffraction pattern from that reported in EP-A-1405856 (referred to as “LNnT polymorph III”).
Crystallization or recrystallization is one of the simplest and cheapest methods to separate a product from contaminants and obtain a pure substance. In addition, providing one or more crystalline modifications (polymorphs) of a solid compound is an important factor in product development, because the different crystalline forms affect the compound's properties—for example, thermodynamic stability, solubility, density, hygroscopicity, electrical properties (such as dielectric constant, conductivity), mechanical properties (such as friability, hardness, breaking strength, elasticity), optical properties (such as colour, transparency, refraction), etc.—diversely. Polymorphs enlarge the repertoire of materials that a scientist has available for improving the product's characteristics.
For this reason, ways have been sought for obtaining other polymorphs of LNnT which may be easier or less expensive to produce in crystalline form.